NASA scientist: Jury’s out on climate link to icy extremes

Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, is the agency’s acting senior climate adviser. His position is new, aimed at sharing their observations of climate change with decision makers. He spoke with the Houston Chronicle about how climate change factors into the winter storm that hobbled the region.

The interview has been edited for clarity and length.

Q: How should we be thinking about this?

A: The basic thing that’s relevant for trying to understand what happens during the wintertime is this notion of this jet stream. It comes from west to east all around the northern hemisphere, generally from the Pacific across America to Europe.

That jet stream is often narrow. The pattern that it has is basically straight around so that it looks like a halo, or it’s very wavy. It goes across at around about the U.S.-Canada border.

They’re two different kind of conditions for the wintertime: When the jet stream is very straight, the latitudes south of that have quite a balmy winter, and places north have quite cold winters.

When it becomes very wavy, like you’ve got a skipping rope, then you get these kind of unseasonable things. Very big cold excursions come south and very warm excursions go north. Both are shocks to the system.

At the edge of that cold band, the cold is now intersecting with the warm tropical air. You get this arctic blast, the temperatures you’re suffering under right now.

Q: How does climate change factor in?

A: Scientists are really trying to dig into what makes one winter different from another, what sets up this pattern of waviness or not.

People look at the temperature gradients at the surface. We know that, during the winter, the Arctic has warmed up a lot. The temperature difference between the tropics and the poles has actually gone down a little bit. There’s some indication that that will make the situation slightly more wavy.

Then there’s other data that suggests that if you go higher up in the atmosphere, the situation reverses, and that would suggest less waviness.

Q: So it’s not clear yet how global warming will impact winters?

A: People rightly say this is an active area of research. Climate change is very real. Temperatures have increased by more than a degree since the 19th century, and three times as fast in the Arctic, and that’s because of changes in greenhouse gases. Those greenhouse gases have impacts all the way through the system.

We expect that weather systems and the waviness of the jet stream will all be impacted by these very large-scale changes.

But often there are multiple pathways by which you can have an effect. So this surface temperature gradient is one pathway, the gradients higher up are another pathway, stuff that’s coming out of the tropics is yes another pathway. Each of those mechanisms and processes are complicated.

The question that people are asking climatologists is: Are these things getting more frequent? It’s not true that winters are getting colder or that we’re getting necessarily more of these cold air outbreaks on average. But there is this research that is looking at the waviness.

Q: People tend to say climate change causes more extreme weather.

A: They do say that but it’s not correct. An outbreak of tornadoes is obviously very extreme but it’s totally different physics and understanding than a cold air outbreak like this.

A hurricane is also an extreme event. A hail storm is an extreme event. It doesn’t make any sense to say that all extremes are going to change because of global warming or they’re all going to go in one direction. You have to look at the extremes themselves.

Some kinds of extremes you do find that there’s a contribution from climate change, so intense rainfall events, like you had with Harvey. Tornado outbreaks, the jury is still out. Ice storms, jury is still out.

Q: How should Houston prepare?

A: There isn’t a prediction that Houston is going to see more of these in the future. But you’ve seen these before, you’re seeing this one, so it makes sense that you should be more resilient. How do you make systems resilient to not just climate change, but climate itself ? Those are some very interesting questions.

Part of what you’re feeling is a weather extreme that’s turned into a disaster. That turning into a disaster thing is not the fault of the weather, it’s the fault of the system that has been put under pressure by the weather.